The field of the present invention is braking systems and more specifically disc brake systems generally employed with motorcycles.
In conventional disc brake systems for motorcycles, the brake disc is installed on one or both sides of the wheel hub. These discs are generally exposed to open air so that the heat of friction generated during braking is dissipated at a sufficient rate by the movement of the disc or discs through the air.
Either by design choice or responsive to certain intended applications of the brake, the brake disc may be enclosed between the hub and a side panel. The brake is then shielded from dirt, water and the like to generally reduce wear. In such enclosed systems, the enclosure also acts to shield the brake disc from the open air. Consequently, heat dissipation is reduced. Conventionally, such shielded disc brakes have been made larger than the braking requirements would suggest to reduce the concentration of heat and to increase heat dissipation. Additionally, ventilating of the disc itself has been employed to increase dissipation.
As it is always advantageous to avoid excessive unsprung weight on a vehicle and as it is also advantageous to use small, light components on motorcycles, reduction in the overall size of a disc braking system is considered beneficial. In the event that shielding of a brake disc is also desired, the requirement for larger discs to accommodate the reduced heat dissipation accompanying shielding comes into conflict with the overall goal of reducing component weight. Thus, increased weight has generally been accepted as an unavoidable liability associated with shielded disc brake designs.
The incorporation of intricate features on the disc such as employed with ventilated discs to increase cooling efficiency also has drawbacks. The disc must necessarily be made of thick metal rather than thin metal in view of heat mass considerations. Consequently, the use of even more material in the disc for cooling features is not advantageous for weight considerations. Greater design intricacy also can create problems regarding fabrication and assembly.
Another difficulty associated with brake discs is the mounting of these discs to the hub. When additional cooling features or increased disc diameter are required, it is advantageous to mount the disc at its periphery so that the caliper member may be placed inside to interfere as little as possible with any cooling mechanism or air flow. Furthermore, placement of the calipers on the inside is advantageous on a motorcycle where compact design is important. The earlier mounting design of such externally supported discs is illustrated in FIG. 1 of the drawings. In FIG. 1, a brake disc a is fixed to a mounting boss b on the hub by means of a rod or bolt c extending through a mounting hole d in the brake disc a. An enlarged mounting boss e on the brake disc a was employed to meet with the mounting boss b through which the bolt c passed. The prior art device illustrated in FIG. 1 required that the bolt c be placed under substantial stress during braking. Such designs generally require more component parts and have a tendency to prevent the free thermal expansion of the disc in the radially outward direction.